Bash for statement

Linux_Kidd · 11-13-2012, 04:32 PM

so i have a Q,
i run a find command to find all files that are "ASCII" and output their full path to a file.

then i run

Code:

for i in `cat all-ascii-files`; do grep -P '\d{3}-\d{3}-\d{3}' $i >> out.txt; done

but something odd happens, i will get some stdout messages that some files are not there "no such file or directory", then the cursor sits there not at a prompt (cant see prompt), but when i hit enter i get a Exit 1 status code for the above "for" statement. why?

unSpawn · 11-13-2012, 04:34 PM

For vs while loop.

pixellany · 11-13-2012, 08:53 PM

I think that was a hint to try this construct:

Code:

while read i; do
     put your commands here
     and here
done < filename

Linux_Kidd · 11-13-2012, 09:01 PM

what do you mean? i dont always get a Exit 1 when using 'for' loops with this input file, so i dont understand why i get this Exit code.

i looked up the diffs between 'for' and 'while' loops and what i have looks ok.

so from bash prompt its

Code:

[server]# while read i; do grep 'whatever' $i; done < all-ascii-files >> outfile

why is this diff than my 'for' loop?

catkin · 11-13-2012, 09:02 PM

You could try modifying the code to print the file names passed to grep and then examine all-ascii-files to see what is the name of the file causing the problem

Code:

for i in `cat all-ascii-files`; do
    echo "DEBUG: i is '$i'"
    grep -P '\d{3}-\d{3}-\d{3}' $i >> out.txt
done

Linux_Kidd · 11-13-2012, 09:07 PM

why would a file name cause an Exit 1? if the file does not exist then the grep simply gives error to stdout "no such file or directory" and the 'for' loop continues.

i can see if the last entry in the file is a file that does not exist then grep exits with a Exit 1 code, but why do i see the command line "script" exit on stdout only when i type a key?

Linux_Kidd · 11-13-2012, 09:36 PM

Quote:

Originally Posted by catkin

You could try modifying the code to print the file names passed to grep and then examine all-ascii-files to see what is the name of the file causing the problem

Code:

for i in `cat all-ascii-files`; do
    echo "DEBUG: i is '$i'"
    grep -P '\d{3}-\d{3}-\d{3}' $i >> out.txt
done

i did the test slightly different, i grep'd for something i knew would be no match, wc -l for input and output files are exactly the same. the Exit 1 i see must be grep failing the match when grep'ing the last $i ??

i just dont understand why i see the Exit status after hitting a key.

unSpawn · 11-14-2012, 06:32 AM

It's due to the IFS.
Use

Code:

cat all-ascii-files|while read ITEM; do grep -P '\d{3}-\d{3}-\d{3}' "${ITEM}" >> out.txt; done

Linux_Kidd · 11-14-2012, 08:18 AM

Quote:

Originally Posted by unSpawn

It's due to the IFS.
Use

Code:

cat all-ascii-files|while read ITEM; do grep -P '\d{3}-\d{3}-\d{3}' "${ITEM}" >> out.txt; done

hmmm, i still get Exit 1 status when it finishes

Code:

[1]+ Exit 1                  cat all-ascii-file | while read ITEM; do
    grep -P '\d{3}-\d{3}-\d{3}' "${ITEM}" >> junk.out;
done

so, it seems that the Exit 1 status code is from grep not finding anything on the last $ITEM it looks at. i grep'd a file for non-existent string and $?=1, but grep for a known match and $?=0.

but correct me if i am wrong, the reason i see the odd way job finishing when using 'for' loop is due to IFS? which IFS causes that?

thanks for the help, its be a learning session for me.

unSpawn · 11-14-2012, 08:39 AM

Quote:

Originally Posted by Linux_Kidd

Code:

[1]+ Exit 1

This says you either ran your code in the background (bg, ampersand) or some character got interpreted as a backgrounding command?

Code:

cat all-ascii-files|while read ITEM; do [ -f "${ITEM}" ] || echo "epic fail \""${ITEM}"\""; done

Quote:

Originally Posted by Linux_Kidd

the reason i see the odd way job finishing when using 'for' loop is due to IFS? which IFS causes that?

Spaces, mostly:

Code:

echo -en "Crack Hitler\nBe Aggressive\nEvidence\n" >> /tmp/listing
# * FNM song titles, obviously.
for ITEM in `cat /tmp/listing`; do echo "${ITEM}"; done
cat /tmp/listing | while read ITEM; do echo "${ITEM}"; done

Also see 'man bash': IFS.

Linux_Kidd · 11-14-2012, 10:30 AM

yes, my very bad, i am & them.